136 ADAPTATIONS. OECOLOGICAL CLASSIFICATION SECT, in 



deciduous leaves, and ' whose conditions of life are, according to the season of 

 the year, alternately those of hygrophytes and of xerpphytes ' ; the structure 

 of their perennial parts is xerophilous, and that of their parts that are present 

 only in the wet season is hygrophilous. Tropophytes as a whole are included in 

 mesophytes (a term also employed by Schimper), as are Schimper's hygrophytes. 

 The cold-temperate flora is mainly tropophilous. The term tropophilous is a very 

 serviceable one as applied to those plants that shed their assimilating organs during 

 the unfavourable season, but there is no group of tropophytes contrasting with those 

 of hydrophytes and xerophytes ; for there are tropophilous hygrophytes and 

 tropophilous xerophytes, as Schimper's own words in various passages indicate. 



In accordance with the considerations given in the present and previous 

 chapters the following oecological classes 1 may be distinguished : 



A. The soil (in the widest sense) is very wet, and the abundant water 

 is available to the plant (at least in Class i), the formations are therefore 

 more or less hydrophilous : 



Class i. Hydrophytes (of formations in water). Section IV. 

 Class 2. Helophytes (of formations in marsh). Section V. 



B. The soil is physiologically dry, i. e. contains water which is available 

 to the plant only to a slight extent ; the formations are therefore essen- 

 tially composed of xerophilous species : 



Class 3. Oxylophytes (of formations on sour (acid) soil). Section VI. 

 Class 4. Psychrophytes (of formations on cold soil). Section IX. 

 Class 5. Halophytes (of formations on saline soil). Section VII. 



C. The soil is physically dry, and its slight power of retaining water 

 determines the vegetation, the climate being of secondary import ; the 

 formations are therefore likewise xerophilous : 



Class 6. Lithophytes (of formations on rocks). Section VIII. 

 Class 7. Psammophytes (of formations on sand and gravel). Sect. X. 

 Class 8. Chersophytes (of formations on waste land). Sect. XII. 



D. The climate is very dry and decides the character of the 

 vegetation ; the properties of the soil are dominated by climate ; the 

 formations are also xerophilous : 



Class 9. Eremophytes (of formations on desert and steppe). Sect. 

 XI. 



Class 10. Psilophytes (of formations on savannah). Section XIII. 

 Class n. Sclerophyllous formations (bush and forest). Sect. XIV. 



E. The soil is physically or physically dry : 



Class 12. Coniferous formations (forest). Section XV. 



F. Soil and climate favour the development of mesophilous forma- 

 tions : 



Class 13. Mesophytes. Section XVI. 



* Concerning the classification of plant-communities, reference should be made 

 to Clements, 19040 ; and regarding nomenclature to Clements, 1902 a and b. 



